nanogrids: evolving our electricity systems from the bottom up

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Nanogrids: Evolving our electricity systems from the bottom up

Bruce Nordman Lawrence Berkeley National Laboratory

January 25, 2011

BNordman@LBL.gov — eetd.LBL.gov/ea/nordman

Darnell Green Building Power Forum

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Overview

•  What is a Nanogrid?

•  Relation to other grids

•  Examples

•  Implementation

•  The way forward

This an initial proposal, not a final design

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Examples

No communications •  Vehicles – 12 V, 42 V, … •  eMerge – 24 V, 380 V •  Downstream of UPS – 115 VAC

With communications •  Universal Serial Bus, USB – 5 V •  Power over Ethernet, PoE – 48 V •  Proprietary systems

Power adapter systems •  Universal Power Adapter for Mobile Devices, UPAMD – IEEE •  Greenplug, Inc. •  Wireless technologies

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What is a Nanogrid?

“A (very) small electricity domain”

•  Like a microgrid, only (much) smaller

•  Has a single physical layer (voltage; usually DC)

•  May have control

•  Is a single administrative, reliability, and price domain

•  Can interoperate with other (nano, micro) grids through gateways

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Nanogrid details

•  Must have at least one load*

•  Must have a gateway* –  Can be intermittently connected –  Supply always via a gateway

•  Only implement power distribution –  Devices control themselves for functionality

•  Can be highly dynamic in connected devices, power flow quantity (and direction), …

•  Range in functionality of controls, gateways

•  Loads usually < 100 W, sometimes < 1 W

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Controller

•  Can have ability to grant or revoke power to loads

•  Negotiates with other grids through gateways

•  Sets prices

•  Manages storage

•  Is the authority within the grid

•  (Should) Provide minimal power to loads at all times to maintain communications ability

•  Deals with loads that do not communicate

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Gateways

•  Can be one-way or two-way (for power)

•  Most functional when communications exist

•  Can be to a nanogrid, microgrid, or the megagrid

•  Have a capacity limit

•  Exchange voltage: ???

•  Only information that passes across gateway is price, capacity, and availability

•  Perhaps storage is just a (special) gateway?

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Price

•  Not required — but really useful

•  Basic mechanism for devices to express preferences

•  Can be unitary or a time series forecast

•  Is local only to the nanogrid

•  Used in deciding when to –  exchange power across gateways –  add to or withdraw from storage

•  Exchange losses dictate differential ‘buying’ and ‘selling’ prices (gateway and storage)

•  Gateways may track energy flows and prices

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Relation to other grids

•  Macrogrid (megagrid) –  Large –  No direct coordination between sources and loads –  Oversizing and diversity enable this

•  As grids get smaller –  Potential for supply/demand imbalances increase –  Need for coordination grows –  Off-grid operation requires local generation or

storage –  Advances in communications technology enables

coordination not before possible

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Microgrids

•  better integrate local (distributed) generation

•  optimize multiple-output energy systems (e.g. combined heat and power, CHP)

•  better integrate local storage

•  provide a variety of voltages, including DC

•  provide a variety of quality and reliability options.

•  operate independently of the macrogrid (or connected)

•  hide microgrid details from the macrogrid

Nanogrids implement only some of these

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Microgrids vs. Nanogrids

•  Few

•  Building/campus scale

•  Multiple voltage, reliability domains

•  Includes generation

•  Have to deal with implementation issues

•  Many

•  Few connected devices

•  Single voltage, reliability domain

•  No generation

•  Already works!

•  Bottom-up approaches are more deployable, flexible, cost-effective, functional

•  Nanogrids can enable a “better grid” faster and cheaper than the “smart grid” (though they can co-exist)

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Inspiration

•  Existing technology •  Modeling network architecture on Internet

•  Randy Katz et al., UCB; “LoCal” – local.cs.berkeley.edu •  Developing country needs; off-grid households

•  Eric Brewer, UCB; TIER – tier.cs.berkeley.edu Technology and Infrastructure for Emerging Regions

Network of networks ! Internet — Network of grids ! Intergrid photos: Colombia University

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Examples

No communications •  Vehicles – 12 V, 42 V, … •  eMerge – 24 V, 380 V •  Downstream of UPS – 115 VAC

With communications •  Universal Serial Bus, USB – 5 V •  Power over Ethernet, PoE – 48 V •  Proprietary systems

Power adapter systems •  Universal Power Adapter for Mobile Devices, UPAMD – IEEE •  Greenplug, Inc. •  Wireless technologies

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Implementation

•  Will be used because they are convenient

•  Enable easy sharing of (surplus) local generation

•  May (or may not) have efficiency advantages

•  Most NG connected to the macrogrid (intermittently) –  Even vehicles will be

•  Price mechanism ensures that all power exchanges are mutually beneficial

•  Gateways have “friction” — this enhances stability

•  Using same technologies in many domains ensures that they are cheap and available for very poor

–  Example: proliferation of mobile phones

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Village example

•  Start with single house – car battery recharged every few days –  Light, phone charger, TV, ??? –  Add local generation – PV, wind, …

•  Neighbors do same –  Interconnect two houses

•  School gets PV –  More variable demand

•  Eventually all houses, businesses connected in a mesh –  Can consider when topology should be changed

•  Existence of generation, storage, households, connections all dynamic

•  Can later add grid connection

B PV

PV

PV

PV

B

B

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Communication

•  Ideally use functional communication path for power coordination, e.g. USB, PoE

•  Otherwise need simple, robust, slow physical layers

•  Single physical layer for power coordination within a NG

•  At gateways need standard communication –  G.hn? Internet Zero? –  Need single gateway protocol / physical layer

•  All communication only requires data links –  not (complicated) network infrastructure

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The way forward

•  Better document existing nanogrids –  Capabilities, uses, …

•  Define a “meta-architecture” for operation, gateways, prices

•  Define specific gateways (voltage, communication)

•  Define nanogrid implementation for existing technologies

•  Always keep power distribution and functionality separate

•  Identify promising applications

•  Demonstrate, document, market

•  Bring (more, better) nanogrids to the neediest

•  Test price mechanism

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Nanogrids and the Smart Grid

•  Nanogrids can (are) implemented only locally

•  Nanogrids provide obvious benefit to users –  Ride on functional advantages for cost, motivation –  Benefits are immediate

•  Nanogrids enable easy evolution of technology, use

•  Nanogrids can interoperate with a smart(er) grid

•  Nanogrids are bottom-up and de-centralized –  SG is top-down, centralized

•  Smart Grid should end at the meter

•  Smart Grid should use price/forecast dominantly –  Only deviate when clearly needed / beneficial

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Summary

•  Nanogrids exist and are widespread

•  They have many advantages –  Likely better efficiency for native DC loads –  Easier (cheaper) renewables integration

•  Can help us quickly evolve our electricity system

Slide 20 of 20 Thank you